High precision electrical resistor device with minimized inductance



nited States Patent HIGH PRECISION ELECTRICAL RESISTOR DEVICE WITH MINIMIZED INDUCTANCE Bernard M. Gordon, Newton, and Robert P. Talambiras, Cambridge, Mass., assignors to Epsco, Incorporated, Boston, Mass., a corporation of Massachusetts Application April 26, 1956, Serial No. 580,779

2 Claims. (Cl. 338-62) The invention relates to'an electrical resistor device, and more particularly to an electrical resistor device of the wire wound type with minimized inductance.

Heretofore, resistor devices have been produced formedof a wire strand which is coiled about a core body. Such devices have been used in making high precision resistors with high heat dissipation and power ratings. Because of their construction, such resistors, however, have an electrical inductance which in many cases is not desirable. In order to minimize the inductive effect of the windings, such prior art devices have utilized adjacent coil sections which are wound in opposite directions. However, because of the low coupling attained between such sections, this method has not been able to reduce the inductance to the degree desired. With the development of the electronic art, such residual inductance made these resistors unsatisfactory, especially for use in computers and other devices utilizing pulses of short duration and high frequency.

A principal object of the invention is to provide a new and improved electrical resistor device of the wire wound type with a minimized inductance.

Another object of the invention is to provide a new and improved electrical resistor device of the wire wound type which is simple and inexpensive in construction and minimizes inductance.

Another object of the invention is to provide a wire wound electrical resistor device which is highly efficient in operation and maintains substantially all the advantages of a wire wound resistor, while having its inductance minimized.

The above objects as well as many other objects of the invention are achieved by providing a wire wound resistor provided with a closely coupled short circuited secondary winding. The secondary winding short circuits the coupled inductance of the resistor coil leaving a minimized effective inductance due to the leakage flux. The leakage flux may be further reduced by providing the resistor with adjacent coil sections wound in opposite directions so that their leakage inductances are in opposed relationships. The increased capacitance due to the close coupling of the resistor winding with the secondary winding is of reduced efiectiveness. since the capacitances of each of the coil sections are connected in series with each other.

Because the winding capacitance of low resistance wire wound devices is usually negligible, the increased capacitance due to the secondary winding is also negligible, while the decrease in the inductance of the device is appreciable and important.

The invention will be most readily understood from the following detailed description of a representative embodiment thereof, reference for this purpose being had to the accompanying drawings, in which:

Figure l is a side elevational view of a wire wound resistor device embodying the invention and having parts broken away,

Figure 2 illustrates in schematic form the resistor device shown in Figure 1, and

Figure 3 illustrates in schematic form an equivalent diagram of the effective parameters of the resistor device represented by Figure 2.

Like reference numerals designate like parts throughout the several views.

The Figure 1 discloses an electrical resistor device 10 of the wire wound type embodying the invention.

The resistor device 10 comprises a supporting or core body 12 having a hollow cylindrical portion 14 forming sections 16 separated and terminated by disc portions 18. The disc portions 18 may be provided with interconnecting slots 20. The core body 12 is preferably made of an electrical insulating material.

Each of the sections 16 of the core body 12 has an outer cylindrical surface22. These surfaces 22 are adjacently positioned and coaxially displaced from each other, and are separated by the discs 18.

Each of the outer surfaces 22 of the sections 16 is provided with a layer or coating 24 of an electrically conductive material such as silver. The coating 24 may be applied by painting, spraying, or by any of the other well known means. The coatings 24 of the respective sections 16 are electrically insulated from each other by the disc portions 18 of the core device 12.

An electrical resistance element 26 which may be of the wire type commonly used, is wound about the respective sections 16 to produce resistor coils 28, 30, 32. The resistorcoil 28 may be formed by passing the wire element 26 in the clockwise direction about the outer surface 22 of the end section 16over its coating 24. The element 26 can then be passed through the communicating slot 20 of the disc portion 18 to form the coil 30 by being wound in the counter-clockwise direction about the cylindrical outer surface 22 of the intermediate section 16 over its conductive coating 24. In a like manner, the next adjacent or end resistor coil 32 may be formed by passing the element 26 through the communicating slot 20 of the disc 18 and winding it in the clockwise direction about the outer surface 22 of the section 16 over its conductive coating 24. By this process, a resistor device can be formed with an desired member of coil sections. a

In order to prevent short circuiting of the resistor element 26 between its turns, it may be provided with the usual insulating coating. If it is desired to provide additional insulation between the resistor coils 28, 30, 32 and their conductive coatings 24, an intermediate electrical insulating coating 34 may be provided over each of the conductive layers 24. Such an insulating coating 34, however, should be made as thin as possible to minimize the separation between the conductivecoatings 24 and their resistor coils 28, 30, 32, while still providing the desired electrical insulation.

Refer to Figure 2 which illustrates in schematic form the electrical resistor device 10 which comprises the resistor coils 28, 30, 32' connected in series between the input and output terminations 36 and 38. Each of the resistor coils 28, 30, 32 are effectively the primary winding of a transformer and may be represented by a resistance component R, leakage inductance component L and a coupled inductance component L which is coupled with the secondary winding formed by the conductive layer 24, and the capacitance C between the windings of the resistor coils.

It is noted that the coupled inductance L is increased and the leakage inductance is reduced or minimized as the coupling of each of the resistor coils 28, 30, 32 is increased with its conductive layer 24. With the increase in the proximity and coupling between the coils and their conductive coatings 24, the capacitance C between the turns of the windings 28, 30, 32 also increases. The increase in this capacitance, however, is negligible since the respective capacitances C of each of the resistor coils are connected in series (see Figures 2 and 3), reducing the value of the total capacitance between the terminals 36, 38.

The Figure 3 is an equivalent representation of the schematic diagram of Figure 2. Since the secondary windings 24 are short circuited, this has the effect of eliminating the coupled inductances L as shown in the circuit of Figure 3. The remaining representation for each of the coils 28, 30, 32 comprises a resistor component R connected in series with the leakage inductance L which is bridged by the capacitance C of the resistor coil. It is noted that the leakage inductance L is minimized by the effect of the oppositely wound adjacent coils 28, 30, 32. This arrangement results in the leakage inductance flux of each coil counteracting that of the next adjacent coil, and further minimizes the effective inductance of the device 10.

The wire wound resistor device 10 embodying the invention is highly effective in minimizing the inductive component by utilizing the shorted secondary winding which is closely coupled with a primary winding formed by its resistor coil. It is particularly noted that the resistor coils 28, 30, 32, without the secondary shorting layers 24, are ineffective for achieving the desired minimized inductance when merely wound in opposite directions. This is because the mutual inductance between the adjacent coils, because of their positioning and other such factors, cannot be made sufficiently high to produce the desired results. This device, however, does utilize this effect to further minimize the leakage inductance to the limited extent afforded by this technique.

The wire wound resistor device 10 is particularly useful for low values of resistance up to ten thousand ohms Where its inductance to resistance ratio is greater than the product of its resistance and capacitance. Of course, the many applications of such a resistor device and the advantages of using a resistor with minimized inductance will be evident to those skilled in the electrical art.

While this invention has been described and illustrated with reference to a specific embodiment, it is to be understood that the invention is capable of various modifications and applications, not departing essentially from the spirit thereof, and which will become apparent to those skilled in the art.

What is claimed is:

1. An electrical resistor device with minimized inductance comprising an insulator core body having a plurality of separate adjacent coaxially displaced cylindrical outer surfaces each adapted to receive a resistor winding thereabout, each of said outer surfaces of said core body being provided with an electrically conductive coating forming a low resistance secondary winding, said coatings being electrically insulated from each other, and an electrical resistance wire element forming series connected primary windings wound respectively about said outer surfaces of said body over their said conductive coatings and inductively coupled with said secondary windings for minimizing the inductance of said device, said resistance element being electrically insulated from and unconnected with said conductive coatings, each of the windings of said resistance element being wound in a direction counter to the direction of its adjacent windings.

2. An electrical resistor device with minimized inductance comprising an insulator core body having a plurality of separate adjacent coaxially displaced cylindrical outer surfaces each adapted to receive a resistor winding thereabout maximizing the mutual inductance of said windings, each of said outer surfaces of said core body being provided with an electrically conductive metallic coating forming a shorted secondary winding for minimizing inductance of the device, said coatings being electrically insulated from each other, and-an electrical resistance wire element forming series connected windings wound respectively about said outer surfaces of said body over their said conductive coatings, said resistance element being electrically insulated from and unconnected with said conductive coatings, said windings being closely positioned over their said conductive coatings to maximize their magnetic coupling and minimize leakage inductance, each of the windings of said resistance element being wound in a direction counter to the direction of its adjacent windings to counteract and minimize the leakage inductance of said windings, the capacitance of each of said windings being effectively in series to minimize the total capacity of the device.

References Cited in the file of this patent UNITED STATES PATENTS 

